Electronics & Communication
Technologies
-Micro-Electro-Mechanical Systems and its
Fabrication
Introduction
Micro-electro-mechanical systems (MEMS) have numerous
applications in the field of aeronautical, space, biomedical
and automobile industries. MEMS device basically consists
of sensors for detection of physical parameters, signal
processing/conditioning circuits for converting them
to current/voltage levels and an actuator for carrying
out required operation/correction. These devices are
fabricated on silicon substrate using micro-machining
technology. The basic building blocks of sensors and
actuators are microstructures such as cantilever beams,
diaphragms, bridges, suspended membranes, etc. and fabricated
using 'bulk micro machining' or 'surface micro machining'
technology. These microstructures being delicate, requires
very careful packaging and handling to avoid possible
damages. In order to over come this problem, a new technique
to form MEMS microstructure several microns below the
surface of the silicon wafers. Has been developed. This
technique is termed as 'recessed microstructure'
MEMS device is formed in the cavity
of the substrate (as a Recessed Microstructure) through
a series of machining steps. The semiconductor substrate
generally comprises of microcrystalline silicone with
a surface oxide layer. The surface may be doped or undoped,
depending on the type of MEMS to be formed within the
cavity as well as the electronic circuitry to be formed.
One or more open cavities are formed after subjecting
the substrate to lithography and etching. The substrate
is then subjected to reoxidisation followed by further
lithography and oxide etching to obtain the first functional
level of MEMS. This is is subjected to P power(4) diffusion
and subsequently formed by depositing a first layer
of a micromachinable material which is also a conductive
material. This layer is micromachined and etched to
form one or more functional elements of the MEMS. These
elements are suitably joined to form functional components
like sensors or actuators. MEMS can also be integrated
with electronic circuitry (e.g. CMOS, BiCMOS or bipolar
electronic circuitry ) Figure 1 shows an enlarged schematic
cross-sectional view of conventional MEMS substrate
prepared by bulk micromachining Figure 2 shows an enlarged
schematic cross-sectional view of conventional MEMS
substrate prepared by surface micromachining Figure
3 shows an enlarged schematic cross-sectional view of
newly developedl MEMS substrate with a recessed microstructure
provided therein.
Salient features:
The newly developed process enables easy packaging
and handling of MEMS. Further, a number of difficulties
faced during conventional surface/bulk machining process,
such as, selective etching of sacrificial layer without
reacting with other materials, increased use of materials
for sacrificial layer, additional etching step required
to remove sacrificial layer, increased duration of machining
are eliminated.
Prospective Users: Electronic
control circuits used for various applications in Aeronautical
industry, Chemical industry, Food processing industry,
Metallurgical Industry, Automobile, Space, Railways,
Defence etc. Micro-sensor applications Radio Frequency
(RF) switches
Type of Technology: Electronic
Device
Status of IPR Protection:
Indian Patent Application No. 39/DEL/2003 dated 13.1.2003
with title "Recessed Microstructure Device and
Method of Fabrication Thereof"
Status of Development:
The technology has been demonstrated through the fabrication
of micro relay using the recessed cantilever beam structure.(Figure
4)
Services offered by Technology
Transfer: Know how manual including quality control
procedures Process demonstration as developed Consultancy
Developed by : Dr. Prem
Pal Department: Center for
Applied Research in Electronics
Contact:
Managing Director
Foundation for Innovation and Technology Transfer (FITT)
Indian Institute of Technology, Delhi
Hauz Khas, New Delhi-110016, INDIA
Tel : 91-011-26597167, 26857762, 26581013, 26597153
Fax : 91-011-26851169
E-mail : drkdpn@gmail.com
